Read the following character list:
ALEXANDER SEREBRAKOFF, a retired professor
HELENA, his wife, 27 years old
SONIA, his daughter by a former marriage MME.
VOITSKAYA, widow, mother of Serebrakoff's first wife
IVAN, her son
MICHAEL ASTROFF, a doctor
ILIA TELEGIN, an impoverished landowner
MARINA, an old woman
A WORKMAN
What is the relationship between Helena and Sonia?
A. doctor and patient
B. professor and student
C. stepmother and stepdaughter
D. mother and daughter